You can use analogies to everyday objects and there are a variety of things you can use in that way, such as pebbles and peas to illustrate moles, because they have different masses. Certainly getting them to think about that and then to be comfortable in translating that into a whole lot of different elements you might be comparing.
Something you can do visually in the lecture theatre is to take in some things you wish to connect and make up an item. Or in PhET, for example, there’s a little activity you can do making sandwiches and you can work out how much you need of which one and whether you’ve got something that’s there in excess or something that’s limiting. It's based on the molar ratios or the stoichiometric coefficients, which in turn are based on the number of moles reacting.
Students come in, like all of us, trying to apply macroscopic analogies to everything – (the billiard balls colliding and similar things) and using them as models for atoms. Try to get across that it's a simple analogy but it's not as simple as that in reality. I guess go back a step and try and show that everything is really just a form of energy.
Students tend to think that large-scale analogies are appropriate. For example, billiard balls colliding. Use such analogies but then deconstruct them for an introduction to quantum mechanics.
We describe quantum mechanics for an electron, but when it’s a tennis ball, what would the equation look like? This gives them the idea that the model works for every kind of particle.
Use an analogy for forbidden transitions in phosphorescence: Anecdotes from the movie 'Born American' (1986). American Backpackers cross from Finland into Soviet era Russia and try to get out again!
